This is an open-label, multi-centre, flexible dose study of retigabine immediate release (IR). The study will enroll male and female outpatients (≥ 18 years of age) with partial-onset seizures (POS) who are inadequately controlled on their current monotherapy Antiepileptic Drug (AED). Following a Screening Period of up to 2 weeks, subjects will enter an 8-week Baseline Phase to determine baseline seizure frequency. At the end of the Baseline Phase, subjects who meet or exceed the minimum seizure frequency of 4 partial seizures per 56 days, will enter the Treatment Period (4 weeks Titration, 16 weeks Flexible Dose Evaluation Phase). All subjects will receive retigabine IR starting at 150 mg/day and will be titrated to 600 mg/day by Week 4. From Week 5 onwards, subjects' doses will be maintained between 300 to 1200 mg/day using a flexible dosing regimen to optimise response and tolerability. The maximum duration of the study is approximately 33 weeks (inclusive of a 3 week Taper/Follow-up Phase).